Powder Refill System for 3-Dimensional Printing

ABSTRACT

A powder refill system for a CBAM process that makes changing a powder container simple and maintains the smallest possible distribution change during the print process. The system automates a constantly low trough powder level during a print and reduces the number of times the powder is recirculated. The system uses a sensor to sense the amount of powder in a tray and a compressed air powder application system to force powder into the system. Powder enters the system from a powder bottle mounted upside-down on a plate with an orifice and mixing chamber and a stainless-steel “aeration stone” This is a fitting with porous walls, where porosity is finer than most of particulate matter of the powder being used. Air can enter through the fitting, broken down into microscopic streams, but powder cannot enter back into the air supplying line. The powder aerosol is then used in the printing/flooding process. A mounting plate allows easy replacement of the powder bottle.

This application is related to, and claims priority from, U.S.Provisional Patent Application No. 62/965,089. Application 62/965,089and U.S. Pat. Nos. 9,393,770; 9,776,376; 9,827,754; 9,833,949;10,046,552; 10,252,487; 10,377,080; 10,377,106; 10,384,437; 10,597,249are hereby incorporated by reference in their entireties.

BACKGROUND Field of the Invention

The present invention relates to 3-dimensional (3-D) printing and moreparticularly to powder refill in a 3-D printing machine.

Description of the Problem Solved

Composite-Based Additive Manufacturing (CBAM) is a process wheresections of a 3-dimensional object are printed on substrate sheets(e.g., carbon fiber) section-by-section using an inkjet printer orlithographic techniques. The printing typically uses an aqueous inksolution, but in some embodiments, can use other solutions or inks. Thesubstrates are then flooded with a powder that can be a thermoplasticmaterial, theromoset metal or other powder. A trough is used as thefinal holder of powder before the flooding occurs. The powder comingfrom the trough adheres only to the wet (printed) portions of thesubstrate. Excess powder is removed from the sheets, and the sheets arestacked on top of one-another. The stack is typically compressed andheated causing the powder layers to fuse forming the 3-D object. Excesssolid material can then be removed by abrasion, sand-blasting, chemicalmeans or other removal technique.

In the original CBAM system, the powder trough was filled using a cup(this cup 317 is shown for reference in FIG. 2. This required operatorintervention and constant monitoring of the trough levels by theoperator. The approach used was refilling the trough to the brim, whichmeant that powder was often recirculated many times. Because the cyclonesystem which recirculates the powder after it is vacuumed has a sizecut-off point dependent on the cyclone construction, but certainly abovefive microns, comparisons of the initial particle size distribution ofpowder from the supplier and recycled powder showed that smallerparticles are lost during the recycling process. Additionally, CT scansshowed inconsistencies of powder loads throughout builds (See FIG. 1).Some layers 201 b had more powder than others, while some layers 201 ahad less powder than others. This effect was thought to be related tothe constant change of trough powder level during a print and the changeof particle size distribution. Maintaining the smallest possibledistribution change during a print requires presence of lowest practicaltrough level. It would be extremely advantageous to have a system thatprovides such control.

SUMMARY OF THE INVENTION

The present invention relates to a powder refill system for a CBAMprocess that makes changing a powder container simple and maintains thesmallest possible distribution change during the print process. Thepowder refill system of the present invention automates a constantly lowtrough powder level during a print and reduces the number of times thepowder is recirculated. The powder refill system uses a sensor to sensethe amount of powder in a tray and a compressed air powder applicationsystem to force powder into the system. Powder enters the system from apowder bottle mounted upside-down on a plate with an orifice and mixingchamber and a stainless-steel “aeration stone” This is a fitting withporous walls, where porosity is finer than most of particulate matter ofthe powder being used. Air can enter through the fitting, broken downinto microscopic streams, but powder cannot enter back into the airsupplying line. The powder aerosol is then used in the printing/floodingprocess. A mounting plate allows easy replacement of the powder bottle.

DESCRIPTION OF THE FIGURES

Attention is now directed to several drawings that illustrate featuresof the present invention.

FIG. 1 shows CT scans of regions where there is more or less powder.

FIG. 2 shows manual powder refilling.

FIG. 3A shows a powder filling device according to the presentinvention.

FIG. 3B shows section A-A of the device of FIG. 3A.

FIG. 4 shows a compressed air control system.

FIG. 5 shows a cyclone powder removal system and powder collector.

FIG. 6 shows an embodiment of a powder container mounting deviceattachable to a powder bottle.

FIG. 7 shows an embodiment of plumbing connections for the presentinvention.

Several figures and illustrations have been provided to aid inunderstanding the present invention. The scope of the present inventionis not limited to what is shown in the figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The powder refill system of the present invention automates a constantlylow trough powder level during a print and reduces the number of timesthe powder is recirculated. The trough is shown in FIG. 2. The totalsystem includes an in-trough powder level sensor 309 and powdercontainer 313. The powder level sensor 309 “looks” downwards at thepowder surface in the trough using an opening in the powder strainer 311and the powder strainer frame 313 mounted on top of the trough 315. Thepowder level sensor can be a range sensor such as the Analog DistanceSensor model GP2Y0A21YK0F manufactured by Sharp. Reading of a longerdistance to the powder surface indicates lower powder level, while ashorter distance corresponds to higher powder level.

Turning to FIGS. 3A-3B, the powder delivery system can be seen. FIG. 3Bshows a section of the assembly in FIG. 3A. The delivery system includesa powder bottle 413 mounted upside-down on a plate 441 with an internalorifice and mixing chamber 417 and a stainless-steel “aeration stone”415 (0.5 micron porosity, commonly used in home beer aeration, 0.5″×1″hollow cylinder). This is a fitting with porous walls, where porosity isfiner than most of particulate matter of the powder being used. Air canenter through the fitting, broken down into microscopic streams, butpowder cannot enter back into the air supplying line. FIG. 4B also showsa handle 411, an exiting powder aerosol flow 419 to a powder collectingbowl (not shown). A dead weight 105 aids in changing powder containersas will be later explained.

Turning to FIG. 4, there is a controller having two valves, an air valve621 and a pinching valve, along with an airflow/pressure regulator 623which are all part of the delivery system. Both valves open whenever thesensor indicates that more powder is needed (i.e., using traditionalfeedback control system principles). The air valve 621 and theairflow/pressure regulator 623 regulate the flow purging through anaeration fitting to fluidize powder in proximity of the orifice,allowing continuous powder feed during a refill. This air flow serves toincrease air pressure inside powder container above atmospheric tofurther assist powder migration. Compressed air enters the system 625 atthe pressure regulator 623. Air flow is controlled by an air flowregulator 627. Conditioned air exits 629 the air flow regulator (627)and is sent to the aeration fitting 415.

Returning to FIG. 3B, powder, passing through the orifice enters amixing chamber 417 where a powder-air suspension is created. The powderaerosol gets carried through a tubing line connected to fitting 631 ofFIG. 4, regulated with the pinching valve, to a tubing line connected tofitting 635, to the powder collecting bowl 741 (to be described in thenext paragraph). The tubing has bleed-in fittings along the lineapproximately every 10″ to add air into the tubing and keep the powdersuspended to avoid clogging.

Turning to FIG. 5, the powder recirculation system (described in U.S.Published Application No. 20180264732) is independent of the powderrefill system component of the machine and serves as a vacuum source andthe powder receptacle. The powder recirculation system includes, but isnot limited to, the cyclone powder separator 737, a powder collectingbowl 741 and a dump valve 743. A vacuum used in the powder deliverysystem originates in the powder collecting bowl into which powder isconveyed. Located on top of the dump valve 743, the powder collectingbowl 741 allows powder to pass from the powder delivery system throughthe dump valve to the atmosphere and into the trough 745. Raising thetrough's powder level stops a call for powder refill and finishes arefill cycle.

FIG. 6 shows the powder container mounting device 100 that eases thepowder container change procedure. It includes a gravity lockingmechanism to prevent significant powder spills, and there is nothreading required to remove/install a container. The device includes amounting plate 101 as a base to where all other parts attach; atrigger/slider 107 biased with a compression spring 109 with a gravitylocking feature and container constraining surfaces; and a dead weightwhich is a solid steel rod 105. The device's powderdispensing/operational position is as shown on FIG. 3A. In order toseparate/remove the powder container from the mounting plate, it isnecessary to flip the entire assembly over. While in the operatingposition, the dead weight migrates down under the gravity force, fallsinto a depression made for this purpose and locks the container so theslider is constrained in place. When the device flipped over for powdercontainer replacement, the dead weight moves back into a cavity insidethe trigger/slider, releases the slider and facilitates powder containerseparation from the device.

To eliminate the need of threading the device onto a powder container, afalse cap is used. The cap itself is screwed on to a powder container asa normal cap would be, but it has no top. Instead, the cap has matingsurfaces that make locking possible.

Once the powder container is in an upright position, the mounting platewith components is above the powder container. An operator holds thedevice by the handle with the right hand (that grip positions the indexfinger in front of the trigger), pulls the trigger and carefully slipsonto or removes the mounting plate and components from top of the powdercontainer (false cap). This process is reversed to attach a new powdercontainer to the mounting plate. After the new powder containerinstallation, the whole assembly is flipped over to bring it into theoperational position shown in FIG. 3A. The mounting plate with the newpowder container is then re-attached to the machine.

FIG. 7 shows an embodiment of plumbing connections for the presentinvention. A pinching valve 847 is shown attached to the powder feedline 851. Bleed-in fittings 849 are shown on the powder feed line onboth sides of the pinching valve.

While the written description above uses the example of sheets as thesubstrate, the principles of the invention described herein have equalapplicability to web or roll based feeding of substrate material.

Several descriptions and illustrations have been presented to aid inunderstanding the present invention. One with skill in the art willrealize that numerous changes and variations may be made withoutdeparting from the spirit of the invention. Each of these changes andvariations is within the scope of the present invention.

We claim:
 1. A powder refill sub-system for a composite-based additivemanufacturing (CBAM) system comprising: a sensor sensing a powderquantity in a powder trough, the sensor coupled to a control system thatactivates a regulated air flow when the powder quantity is sensed to bebelow a threshold; a powder delivery system connected to the regulatedair flow comprising a powder bottle with an orifice, a regulated airflow inward connection comprising a porous surface with porosity finerthat particulate matter of the powder, and an outward connectionconfigured to contain and deliver a powder aerosol; a powder collectingbowl disposed between the powder delivery system and the powder trough;such that air supply through to the porous surface conveys a powderaerosol into a the powder collecting bowl when the sensor detects thatthe powder quantity is below the threshold.
 2. The powder refillsub-system for a CBAM system of claim 1 wherein the powder deliverysystem includes a powder container holder comprising: a mounting plate;a trigger/slider with gravity locking feature and container constrainingsurfaces; a dead weight; a false cap; and the powder container holderhaving an operational state and a refill state, wherein flipping themounting plate over changes from the operation state to the replacementstate and flipping the mounting plate over again changes from thereplacement state to the operational state, wherein, in the operationalstate, the dead weight falls into a depression locking thetrigger/slider, and in the replacement state, the dead weight moves outof the depression releasing the trigger/slider; the false capconstructed to attach to a powder container in the replacement statewhen a trigger on the trigger/slider is pulled.
 3. The powder refillsub-system for a CBAM system of claim 1 further comprising an air valve,a pinching valve, and a pressure regulator that creates the regulatedair flow.
 4. The powder refill sub-system for a CBAM system of claim 3wherein regulated air flow commences by the air valve and the pinchingvalve both opening in response to the sensor detecting powder in thetrough below the threshold.
 5. The powder refill sub-system for a CBAMsystem of claim 1 further comprising first flexible tubing connectingthe regulated airflow to the inward connection, and second flexibletubing connecting the outward connection to the powder collecting bowl.6. The powder refill sub-system for a CBAM system of claim 5 wherein thesecond flexible tubing comprises at least one bleed-in fitting forkeeping powder contained therein in a suspended state.